ceil(3) — Linux manual page


ceil(3)                 Library Functions Manual                 ceil(3)

NAME         top

       ceil, ceilf, ceill - ceiling function: smallest integral value
       not less than argument

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #include <math.h>

       double ceil(double x);
       float ceilf(float x);
       long double ceill(long double x);

   Feature Test Macro Requirements for glibc (see

       ceilf(), ceill():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       These functions return the smallest integral value that is not
       less than x.

       For example, ceil(0.5) is 1.0, and ceil(-0.5) is 0.0.

RETURN VALUE         top

       These functions return the ceiling of x.

       If x is integral, +0, -0, NaN, or infinite, x itself is returned.

ERRORS         top

       No errors occur.  POSIX.1-2001 documents a range error for
       overflows, but see NOTES.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ ceil(), ceilf(), ceill()            │ Thread safety │ MT-Safe │

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

NOTES         top

       SUSv2 and POSIX.1-2001 contain text about overflow (which might
       set errno to ERANGE, or raise an FE_OVERFLOW exception).  In
       practice, the result cannot overflow on any current machine, so
       this error-handling stuff is just nonsense.  (More precisely,
       overflow can happen only when the maximum value of the exponent
       is smaller than the number of mantissa bits.  For the IEEE-754
       standard 32-bit and 64-bit floating-point numbers the maximum
       value of the exponent is 127 (respectively, 1023), and the number
       of mantissa bits including the implicit bit is 24 (respectively,

       The integral value returned by these functions may be too large
       to store in an integer type (int, long, etc.).  To avoid an
       overflow, which will produce undefined results, an application
       should perform a range check on the returned value before
       assigning it to an integer type.

SEE ALSO         top

       floor(3), lrint(3), nearbyint(3), rint(3), round(3), trunc(3)

Linux man-pages (unreleased)     (date)                          ceil(3)

Pages that refer to this page: abs(3)fabs(3)floor(3)lrint(3)lround(3)rint(3)round(3)roundup(3)trunc(3)